Design of a car anti-collision infrared ranging system

With the development of economy, the transportation industry is becoming more and more prosperous. However, the hardware such as road conditions and traffic management cannot keep up. In addition, subjective principles such as overtaking, driving erratic, and misestimating the distance between vehicles have caused frequent traffic accidents. The fundamental measure to solve this problem is to install a device that can automatically track and measure the distance on the moving car and automatically brake within the dangerous distance.

With the development of electronic technology, laser ranging, microwave radar ranging, ultrasonic ranging and infrared ranging have appeared successively . Among them, laser ranging is to detect the distance between two vehicles by irradiating the laser beam on the reflector (the rear of the car) on the front car and reflecting the laser beam back. Due to the influence of factors such as bad weather, violent vibration of the car, wear and pollution of the reflector surface, the detection distance of the reflected laser beam at a certain power is reduced by 1/2 to 1/3 compared with the maximum possible detection distance, which is a great loss and affects the accuracy of detection; the equipment and oscillator circuit parts of microwave radar ranging technology used in military and certain industrial development are expensive, and now there is almost no civilian market; ultrasonic ranging has been studied at home and abroad, but due to the use of special dedicated components , it is expensive and difficult to promote; infrared, as a special light wave, has the basic physical transmission characteristics of light waves - reflection, refraction, scattering, etc., and because its technical difficulty is relatively not great, the ranging system formed is low-cost and has excellent performance, which is convenient for civilian promotion.

The basic principle of distance measurement used in current distance measurement systems is based on measuring time difference, and the main methods of measuring time are "pulse method" and "frequency modulation 2 continuous wave method". Both of these measurement methods are implemented by analog circuits. Due to the influence of device delay, the measurement accuracy is greatly reduced. This article adopts the "counting" method, which is processed by a single-chip microcomputer to greatly improve the measurement accuracy.

Therefore, the infrared distance measurement system studied in this paper has low cost and small size, and uses a new distance measurement principle combined with single-chip microcomputer technology to greatly improve the measurement accuracy; at the same time, this distance measurement system is applied to the automobile anti-collision system, and the vehicle anti-collision test is carried out. The test results show that the system can detect a distance greater than 40m, and the speed of analyzing and judging dangerous situations is fast and the accuracy is high.

2 Basic principles of infrared ranging and establishment of its system

2.1 Basic Principles

The infrared transmitter continuously emits infrared rays with a frequency of 40kHz. After being reflected by obstacles, the infrared receiver receives the reflected wave signal and converts it into an electrical signal. By measuring the time difference t between the transmitted wave and the received reflected wave, the distance s can be calculated:

In the formula, c is the speed of light, generally 3×108m/s.

This article adopts the "counting" method, which is measured by single-chip microcomputer processing. The basic principle is: the infrared transmitter is always in the state of transmitting infrared rays. When the infrared receiver receives the infrared rays reflected by the obstacle for the first time, the single-chip microcomputer gives a counting start signal after circuit processing, and the single-chip microcomputer counter starts counting at a certain frequency; when the infrared receiver receives the reflected infrared rays for the second time, the single-chip microcomputer gives a stop counting pulse after circuit processing, and the counter stops counting. Through programming, the single-chip microcomputer automatically processes, and the time difference t from transmitting infrared rays to receiving infrared rays is obtained by multiplying the pulse period T by the number of pulses n, that is:

Substituting equation (2) into equation (1) yields the distance measurement.

2.2 System establishment

According to the above distance measurement principle, the basic block diagram of the system is designed as shown in Figure 1.

Figure 1 Basic block diagram of infrared ranging system

The infrared transmitting circuit emits infrared rays with a frequency of 40kHz. When encountering obstacles, the infrared rays are diffusely reflected. When the infrared receiving circuit receives the reflected infrared rays for the first time, it gives a signal pulse to the microcontroller, starts the counter in the microcontroller, and the counter is set to enter the counting state; when the receiving circuit receives the infrared rays from the reflector for the second time, it is processed by the microcontroller and gives a signal pulse to stop the counter from counting. The data is latched and then processed by the microcontroller to display the measured distance on the display.

3 Application of infrared ranging in automobile collision avoidance system

3.1 Basic features

The automobile infrared anti-collision system studied in this paper absorbs some characteristics of various rangefinders at home and abroad, and is designed based on the development direction of China's automotive electronics industry and existing electronic technology. It has the following characteristics:

1) The car can automatically and continuously track and display the distance of obstacles while moving;

2) On highways with heavy traffic, the distance between vehicles is generally 30 to 50 meters. This device sets the maximum safety distance to 30 meters. When the detected distance between vehicles is 30 meters, a warning sound is issued to remind the driver to brake;

3) When the detected vehicle distance is 20m, an automatic braking signal will be given; if an automatic braking device is installed, the vehicle will automatically brake and slow down.

3.2 Automobile Infrared Anti-collision System

The circuit diagram of the automobile infrared anti-collision system is shown in Figure 2.

Figure 2 Circuit diagram of the car infrared anti-collision system

The system consists of six parts: transmitting part, receiving part, single chip microcomputer, decoding and display circuit, alarm part and automatic braking and deceleration device.

Transmitter part: It consists of a 40kHz oscillator, a constant current transmitter and a transmitter probe. The oscillator generates narrow pulses with a very small duty cycle. A constant current source is used to provide a current of about 20mA, which reduces power consumption and increases the transmission power. Finally, the infrared rays are focused by the transmitter probe and emitted at a scattering angle of less than 2°.

Receiving part: It is composed of infrared receiving head, first stage amplifying circuit, second stage amplifying circuit, shaping, AGC gain control circuit, etc. After the infrared receiving head receives the signal, it is amplified by the first stage and second stage amplifying circuit, shaped by Schmitt trigger circuit, and sent to the single chip microcomputer for processing. Among them, AGC controls the gain of the receiving circuit to ensure constant amplitude output.

Single chip microcomputer: It is composed of a clock oscillator and a single chip microcomputer. After programming, the single chip microcomputer can automatically count, calculate the time t and measure the distance s, and continuously output the measured distance to the display device. At the same time, it generates an alarm signal when the distance between cars is 30m and an automatic brake deceleration signal when the distance between cars is 20m.

Decoding and display circuit: It consists of a decoding circuit and a display. The distance signal output by the microcontroller is decoded by the decoder and displayed on the display.

The distance between the car and obstacles can be dynamically displayed.

Alarm part: It consists of a trigger, a drive circuit and a small speaker. When the distance between vehicles is 30m, the microcontroller sends a signal to the trigger, which sets the trigger to generate a group of pulses. Through the drive circuit, the small speaker sounds an alarm. When the distance is greater than 30m, the trigger is reset and stops generating pulses.

Automatic brake deceleration device: It consists of switch K and automatic brake deceleration device. When the driver thinks it is necessary to use the automatic brake deceleration device, switch K is closed. When the distance between vehicles is less than 20m, the single chip microcomputer provides a signal to start the automatic brake deceleration device to prevent collision.

4 Performance evaluation of automobile infrared collision avoidance system

In order to evaluate the performance of the automobile infrared collision avoidance system, including the performance of detecting obstacle distance and relative speed, two tests are adopted: static distance detection and dynamic detection when driving on the highway.

4.1 Still Object Distance Detection Test

An ordinary car is placed in front of a test car equipped with an infrared anti-collision system. The test car drives towards the ordinary car at a speed of 30km/h from a distance of 100m. When the distance is greater than 40m, it displays 0; when the distance is less than 40m, the data displayed on the display changes continuously; when the distance between cars is 30m, the alarm starts to sound. The experimental results show that it is consistent with the actual distance between cars and the detection results are accurate. The experimental results are shown in Figure 3.

Figure 3 Results of static object distance detection experiment

4.2 Driving dynamics test on highway

The test car and the ordinary car were driving in the same direction on the highway at the same time. Before driving, the two cars kept a distance of 100m. The test car emitted infrared rays to the ordinary car to detect the distance and relative speed between the two cars. The experimental results are shown in Figure 4.

Figure 4 Dynamic test results on the highway

5 Conclusion

This paper adopts a new distance measurement principle to establish an infrared distance measurement system, and studies the application of the infrared distance measurement system in the automobile anti-collision system.

In order to make the measured time difference t accurate, two methods are used to improve the accuracy:

1) The period T of the counting pulse should be very small, reaching the microsecond level;

2) Count the count pulses of N received infrared cycles and calculate the time difference t using the formula t=nT/N, the accuracy is improved to about N times the original.

Of course, in order to make the automobile infrared anti-collision system practical, the following problems need to be solved:

1) How to prevent vehicles on the adjacent lane from having an illusion of being in the wrong lane due to objects on both sides of the road when driving on the side lane;

2) The microcontroller has poor anti-vibration capability, which affects its working reliability;

3) What kind of alarm signal should be sent to prevent the driver from feeling nervous and uneasy;

4) How to further improve the counting frequency of the microcontroller and reduce the error;

5) The detection distance is affected by bad weather, and the infrared loss is large;

6) The dynamic detection distance needs to be further improved.

These problems need further research and discussion. I believe that with the improvement of devices and experimental conditions, these problems will be satisfactorily solved.

In short, this system has a broad market due to its low cost, high accuracy, and multiple functions.